The present invention concerns a method for photopolymerizing episulfides in the presence, as polymerization catalyst, of at least one metal complex, in particular a ruthenium complex, and to the use of such a photopolymerization method for making episulfide based ophthalmic lenses.
The use of ruthenium cyclopentadienyl complexes for anionic photopolymerization of 2-cyanoethylacrylate has been disclosed in U.S. Pat. No. 5,652,280.
Thermal polymerization of episulfides is known from U.S. Pat. No. 5,807,975, EP 761,665, EP 785,194 and EP 942,027. These disclosed polymerization processes need long thermal polymerization cycles.
Photo-initiated cationic polymerization of monoepisulfides is disclosed in article xe2x80x9cPhotocationic cross-linking of poly(2,3-epithiopropyl methacrylate) and Photoinitiated cationic polymerization of its model compoundsxe2x80x9d, M. Tsunooka et al., Journal of Polymer Science: polymer chemistry edition, vol. 22, 2217-2225 (1984). However, the photoiniators used in the polymerization are coloured materials that are not suitable for making optical lens material.
International patent application WO 00/26272 discloses a process for making thio containing resins which comprises polymerizing a composition comprising at least one diepisulfide compound and, as polymerization catalyst, an alkaline metal, alkaline-earth metal or ammonium salt of an acid having a pKa from 0.5 to 14.
Although this later polymerization process leads to fast polymerization of the composition, the process is difficult to control due to the highly exothermic polymerization reaction which may result in a charred resin inappropriate for making optical articles such as ophthalmic lenses.
Thus, one object of the invention is to provide a photopolymerization process of episulfides, in particular diepisulfides, which allows fast and safe polymerization.
Another object of the invention is to provide a fast and safe process for making episulfide based optical articles, in particular ophthalmic lenses.
These and other objects of the invention are achieved by providing a photopolymerization process of episulfides monomers which comprises:
(a) mixing to an episulfide monomer or a mixture of episulfide monomers an effective amount of at least one photopolymerization catalyst selected from (cyclopentadienyl) ruthenium complexes and (cyclopentadienyl) osmium complexes, and an effective amount of at least one co-catalyst selected from phosphonium salts, phosphines and amines; and
(b) irradiating the mixture of (a) with an ultraviolet (UV) radiation to polymerize the mixture.
Preferably, there is also added to the mixture of (a) an effective amount of a co-catalyst selected from the group consisting of phosphorous and amine compounds.
The present invention also contemplates a process for making an optical article which comprises:
(a) filling a mold cavity with a photopolymerizable composition comprising at least one episulfide monomer and an effective amount of a photopolymerization catalyst selected from the group consisting of (cyclopentadienyl) ruthenium complexes and (cyclopendienyl) osmium complexes, and an effective amount of at least one co-catalyst selected from phosphonirum salts, phosphines and amines; and
(b) irradiating the polymerizable composition with an UV radiation for polymerizing the composition at least up to obtention of a self-supporting gel.
Preferably, the composition is subjected to a pre-heating step before irradiation step (b).
Also, preferably, after irradiation step (b), the gellified article is subjected to a post-heating step to achieve full polymerization of the article.